Following a recent trend of a decrease in the weight, thickness, and length of electronic devices, efforts have been made to reduce the size and thickness of terminals, connectors, and the like, and there has been a demand for strength and bending workability. As a result, instead of solid solution strengthening-type copper alloys, such as phosphor bronze or brass of the related art, the need for precipitation strengthening-type copper alloys, such as Corson (Cu—Ni—Si-based) alloy, beryllium copper or copper-titanium alloy, is increasing.
Among the precipitation strengthening-type copper alloys, Corson alloy is an alloy having a solid solubility limit of a nickel silicide compound with respect to copper which significantly varies depending on temperature, and is a kind of precipitation strengthening-type alloy which is cured through quenching and tempering. Corson alloy also has favorable heat resistance or high-temperature strength, has excellently balanced strength and electrical conductivity, has thus far been widely used in a variety of conduction springs, electric cables for high tensile strength, and the like, and, in recent years, has been in increasing use for electronic components, such as terminals and connectors.
Generally, strength and bending workability are conflicting properties, even in Corson alloy, studies have thus far been conducted in order to improve bending workability while maintaining a high strength, and efforts have been widely made in order to improve bending workability by adjusting manufacturing processes, and individually or mutually controlling crystal grain diameter, the number and shape of precipitates, and crystal texture.
In addition, in order to use Corson alloy in a predetermined shape in a variety of electronic components under severe environments, there is a demand for feasible workability, particularly, favorable deep drawing workability and solder resistance to heat separation during use at a high temperature.
PTL 1 discloses a Cu—Ni—Si-based alloy for electronic components which contains 1.0 mass % to 4.0 mass % of Ni, and Si at a concentration of ⅙ to ¼ of that of Ni, has a frequency of twin boundaries (Σ3 boundaries) in the all crystal grain boundaries of 15% to 60%, and has excellently balanced strength and bending workability.
PTL 2 discloses a copper-based precipitation-type alloy plate material for contact materials in which the maximum value of the differences among three tensile strengths of a tensile strength in the rolling direction, a tensile strength in a direction that forms an angle of 45° with the rolling direction, and a tensile strength in a direction that forms an angle of 90° with the rolling direction is 100 MPa or less, and which contains 2 mass % to 4 mass % of Ni, 0.4 mass % to 1 mass % of Si, and, if necessary, an appropriate amount of at least one selected from a group consisting of Mg, Sn, Zn and Cr with a remainder of copper and inevitable impurities. The copper-based precipitation-type alloy plate material for contact materials is manufactured by carrying out an aging heat treatment and then cold rolling at a percentage reduction in thickness of 30% or less on a copper alloy plate material which has been subjected to a solution treatment, and improves the operability of multifunction switches used in electronic devices and the like.
PTL 3 discloses a Corson (Cu—Ni—Si-based) copper alloy plate which has a proof stress of 700 N/mm2 or more, an electric conductivity of 35% IACS or more, and excellent bending workability. This copper alloy plate includes Ni: 2.5% (mass %, the same shall apply hereinafter) to less than 6.0% and Si: 0.5% to less than 1.5% so as to make a mass ratio Ni/Si of Ni to Si in a range of 4 to 5, and, furthermore, Sn: 0.01% to less than 4%, with a remainder of Cu and inevitable impurities, has a crystal texture in which the average crystal grain diameter is 10 μm or less, and the fraction of a cube orientation {001}<100> is 50% or more in a measurement result obtained through SEM-EBSP, and is manufactured by obtaining a solution recrystallization structure through continuous annealing, then, carrying out cold rolling at a working rate of 20% or less and an aging treatment at 400° C. to 600° C. for one hour to eight hours, subsequently, carrying out final cold rolling at a working rate of 1% to 20%, and then carrying out short-time annealing at 400° C. to 550° C. for 30 seconds or less.